Moderate SeveritySafe to drive (short-term)Emissions
P0400 means the engine control unit has detected that exhaust gas recirculation flow is not within the expected range. The EGR system recirculates a portion of exhaust gas back into the intake to lower combustion temperatures and reduce NOx emissions. A blockage or valve failure disrupts this flow.
What does P0400 mean?
P0400 means the engine control unit has detected that exhaust gas recirculation flow is not within the expected range. The EGR system recirculates a portion of exhaust gas back into the intake to lower combustion temperatures and reduce NOx emissions. A blockage or valve failure disrupts this flow.
P0400 is a emissions-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0400 and illuminates the check engine light.
What are the symptoms of P0400?
If your vehicle has triggered P0400, you may notice one or more of these symptoms:
Check engine light on
Rough or unstable idle
Engine knocking or pinging under load
Reduced fuel economy
Failed emissions test (high NOx readings)
Hesitation during acceleration
What causes P0400?
Here are the most common causes of P0400, ranked by how likely they are to be the culprit:
highCarbon-clogged EGR valve
highBlocked EGR passages or cooler
mediumFailed EGR valve (stuck open or closed)
mediumFaulty EGR position sensor or pressure feedback sensor
lowVacuum supply issue to vacuum-operated EGR valve
Is it safe to drive with P0400?
Generally yes, for short-term driving. The vehicle is generally safe to drive in the short term, but EGR faults can cause increased NOx emissions, rough idle, and reduced fuel economy. Repair before the next emissions inspection.
How do you diagnose P0400?
Follow these steps to pinpoint the root cause of P0400:
Check for companion EGR codes (P0401, P0402, P0403) that may help narrow down whether the issue is insufficient flow, excessive flow, or an electrical fault
Remove the EGR valve and visually inspect for carbon buildup. A heavily clogged valve is the most common cause and can be cleaned with carburettor cleaner
With the EGR valve removed, inspect the intake and exhaust passages for carbon blockage. Use a flashlight and probe to check passage diameter
Test the EGR valve operation by applying vacuum (vacuum-operated) or commanding it open with a scan tool (electronic). It should open and close smoothly
If the valve operates correctly, check the DPFE sensor or EGR position sensor readings on the scan tool against manufacturer specifications
How much does P0400 cost to fix?
Repair costs for P0400 vary depending on the root cause and your vehicle. Here are typical estimates:
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Clean EGR valve and passages
€5–€30
€60–€200
€65–€230
Moderate
Replace EGR valve
€60–€350
€60–€250
€120–€600
Moderate
Replace EGR cooler
€100–€400
€150–€500
€250–€900
Professional
Replace DPFE or EGR pressure sensor
€20–€80
€30–€100
€50–€180
Easy
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0400 on specific vehicles
P0400 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:
P0400 on Volkswagen Golf
Volkswagen Golf • 2003-2024
The 1.9 TDI and 2.0 TDI engines are well-known for EGR valve carbon clogging, especially in stop-and-go city driving. The EGR cooler on the 2.0 TDI (CR) can also crack, leading to coolant loss. Regular motorway driving helps keep the EGR cleaner.
What causes P0400 on a Volkswagen Golf?
Volkswagen GolfCarbon-clogged EGR valve on 1.9/2.0 TDI from city driving
Volkswagen GolfEGR cooler failure on 2.0 TDI common rail
P0400 repair cost for Volkswagen Golf
Estimated costs for Volkswagen Golf ownersadjusted higher than average due to Volkswagen-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Clean EGR valve and passages
€6–€33
€66–€220
€72–€253
Moderate
Replace EGR valve
€66–€385
€66–€275
€132–€660
Moderate
Replace EGR cooler
€110–€440
€165–€550
€275–€990
Professional
Replace DPFE or EGR pressure sensor
€22–€88
€33–€110
€55–€198
Easy
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
P0400 on Ford Focus
Ford Focus • 2005-2022
The 1.6 TDCi engine uses a vacuum-actuated EGR valve that is prone to carbon buildup and diaphragm failure. The DPFE (differential pressure feedback) sensor on the 2.0 Duratec petrol engine is a known failure point and is inexpensive to replace.
What causes P0400 on a Ford Focus?
Ford FocusEGR valve diaphragm failure on 1.6 TDCi
Ford FocusDPFE sensor failure on 2.0 Duratec petrol
P0400 on Opel Astra
Opel Astra • 2004-2024
The 1.7 CDTi (Z17DTH/A17DTJ) is very susceptible to EGR clogging, particularly in urban driving. The EGR valve on these engines is electrically operated and can seize in the open position, causing rough idle and excessive smoke.
What causes P0400 on a Opel Astra?
Opel AstraEGR valve seizure on 1.7 CDTi engines
Opel AstraCarbon-blocked EGR passages from short urban trips
P0400 on Peugeot 308
Peugeot 308 • 2007-2024
The 1.6 HDi (DV6) engine shares its EGR system with the Ford 1.6 TDCi and is equally prone to carbon clogging. The 2.0 HDi has a more robust EGR setup but the cooler can develop leaks after 100,000 km.
What causes P0400 on a Peugeot 308?
Peugeot 308Carbon clogging on 1.6 HDi EGR valve
Peugeot 308EGR cooler leak on 2.0 HDi after high mileage
P0400 repair cost for Peugeot 308
Estimated costs for Peugeot 308 ownersadjusted higher than average due to Peugeot-specific parts pricing
Repair
Parts Cost
Labor Cost
Total Estimate
DIY Difficulty
Clean EGR valve and passages
€5–€32
€63–€210
€68–€242
Moderate
Replace EGR valve
€63–€368
€63–€263
€126–€630
Moderate
Replace EGR cooler
€105–€420
€158–€525
€263–€945
Professional
Replace DPFE or EGR pressure sensor
€21–€84
€32–€105
€53–€189
Easy
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related diagnostic codes
These codes are often seen alongside P0400 or indicate related issues:
The Exhaust Gas Recirculation system routes a small amount of exhaust gas back into the engine intake. This lowers combustion temperatures and significantly reduces nitrogen oxide (NOx) emissions, which are a major component of smog.
Can I drive with P0400?
Yes, for a short time. The vehicle will run, but you may notice rough idle, knocking under load, and poor fuel economy. The main risk is failing an emissions test and potentially causing increased engine wear from higher combustion temperatures.
How often does the EGR valve need cleaning?
On diesel engines, EGR cleaning every 40,000 to 60,000 km is advisable due to higher soot levels. Petrol engines accumulate carbon more slowly, but a cleaning every 80,000 to 100,000 km is good preventive maintenance.
What is the difference between P0400 and P0401?
P0400 is a general EGR flow malfunction, meaning the flow is outside the expected range. P0401 specifically means insufficient EGR flow, which is usually caused by a clogged valve or blocked passage. P0400 is less specific about the direction of the fault.
Is it OK to delete or block the EGR valve?
In the EU, blocking or deleting the EGR system is illegal and will cause the vehicle to fail its periodic roadworthiness test (TUV, MOT, ITV, etc.). It also significantly increases NOx emissions. The correct approach is to clean or replace the faulty component.
